CHANGELOG: add note on cryptography
CHANGELOG: add note on cryptography

Point out that the latest version of cryptography is not used on Python 2
due to upstream cryptography dropping support for that EOL Python version.

Signed-off-by: Joshua Lock <edc229f50a11a11cdece0270af6320fb299dca1e@vmware.com>

secure-systems-lab/securesystemslib,secure-systems-lab/securesystemslib